ocr: environment on land and in the sea. Blue whales bear only a single offspring at a time, and two or three years elapse between births. The calf develops for almost eleven months before birth, when it measures about twenty-five feet in length and weighs more than two tons. The mother produces about two hundred pounds of milk a day during the eight-month period she nurses the calf; by the end of this time it is about fifty feet long. Sexual maturity is attained when the whale has grown to 68